The present invention relates to a recirculating document feeder adapted to circulate each document sheet from a stack of such sheets to an exposure position. The feeder is used chiefly for copying machines for automatically repeatedly copying a predetermined number of document sheets one by one in the order of the sheets as stacked.
Recirculating document feeders of this type generally comprise means for supporting a stack of document sheets, means for sending out the sheets from the supporting means one by one, a feed path for transporting the sent-out sheet to an exposure position, and a return path for returning the sheet from the exposure position to the supporting means, as disclosed in U.S. Pat. Nos. 4,169,674, 4,597,570, 4,621,801, 4,368,986 and 4,660,819, and Examined Japanese Patent Publication No. SHO 56-40338. Such known feeders are so adapted that the plurality of sheets as stacked in the supporting means are fed to the exposure position one by one for printing and thereafter returned to the supporting means with the sheet rear ends brought to a specified position therein.
However, the known feeder encounters difficulty when to be used for document sheets of different sizes. When the sheets are returned to the supporting means after printing, the sheet rear ends are in register at the specified position, but the position of the front ends differs from size to size, such that some sheets fail to reach the specified feed position, or document sheets of a particularly size only are feedable with stability. The documents usable are therefore limited in size, and extreme inconvenience is experienced because the document sizes presently in use include A series and B series of JIS standards and other sizes in millimeters or inches and further because documents are fed to the machine as oriented in the direction of the length or width of the sheet.